The HDR (High-dynamic-range imaging) is a photography technique which makes it more capture “range of light” in the image.
It has happened to all of us shooting that way to the beach and the sky is white or, in the middle of the woods, shooting the treetops and branches turn black.
What is happening is that the “amplitude” of the sensors still fail to capture everything that the human eye can see, and if the scene has a lot of range of light is normal to be anything “burned” / under exposed.
With the HDR we can expand this range to any value. You can have the sun in front and a shadow to a basement, in the same picture, and get a blue sky and see the details in the basement.
The HDR is usually composed of multiple exposures and can be done automatically (AEB – auto exposure bracketing) or manual (by varying the exposure times of something “fast” for the blue sky to something slow to get the detail of the basement , for example). It is possible to build a HDR image from only one RAW image
Note: AEB serves to more things than creating HDR images.
To make a manual Exposure Bracketing is highly recommended using a tripod since it involves removing the framework of the machine, look, fit, replace the machine in the environment and this will cause a misalignment of the images. In the case of the AEB, although also the tripod is advisable, depending on the focal length, can be handheld and the software used will re-align the pictures.
There are many software to join multiple pictures and build HDR images. Photoshop of course, photomatix, oloneo, nik hdr, hdr MediaChance, etc. Try it and enjoy the results.
Usually what I do (because I like to HDR’s that result in normal pictures) is to get an image in TIF 32bit and then use Adobe Lightroom for … whatever I want. The resulting images are “bullet proof” in the sense that, being too dark or too light never “burn” in white or “lose detail” in the shadows.